Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $191.91   10.777%   $212.5921   $212.59   $212.60   $212.60  
  Purchase #2 $164.90   4.212%   $171.8456   $171.85   $171.85   $171.80  
  Purchase #3 $48.57   5.833%   $51.4031   $51.40   $51.40   $51.40  
  Purchase #4 $130.74   4.423%   $136.5226   $136.52   $136.50   $136.50  
  Purchase #5 $63.30   9.548%   $69.3439   $69.34   $69.35   $69.30  
  Purchase #6 $17.83   3.834%   $18.5136   $18.51   $18.50   $18.50  
  Purchase #7 $151.93   9.694%   $166.6581   $166.66   $166.65   $166.70  
  7 purchase totals = $769.18       $826.8790   $826.87   $826.85   $826.80